1. Field of the Invention
The present invention relates to a lens shape measuring method and a lens shape measuring apparatus for measuring, in terms of lens shape: a lens frame shape of a spectacle frame; and an outer diameter shape of a template, a dummy lens, or the like.
2. Description of the Related Art
Conventionally there has been a kind of lens shape measuring apparatus for measuring a lens shape for a lens frame and the shape of a spectacle lens. The lens shape measuring apparatus of this kind includes: a lens frame feeler for measuring the inner peripheral surface shape (lens fitting groove (V-shaped groove) shape) of a lens frame of a spectacle frame; and a lens shape feeler for measuring the outer peripheral surface shape of a lens shape of a template, a dummy lens or the like (for example, refer to Japanese Unexamined Patent Application Publication No. H7-164295).
This conventional lens shape measuring apparatus includes: a rotation base mounted rotatably about a vertical rotation axis line; a slider mounted on the rotation base movably forward and backward in a radial direction of rotation about the rotation axis line; the lens frame feeler vertically movably held by the slider, and the lens shape feeler tiltably mounted on the slider.
With this conventional lens shape measuring apparatus, the measurement is performed as follows. Specifically, while the rotation base is horizontally rotated about the rotation axis line, the lens frame feeler is moved along a lens fitting groove of a lens frame or the like in the circumferential direction or the lens shape feeler is moved along the outer peripheral surface of a lens in the circumferential direction. During the movement, the amount of movement of the feeler in the horizontal direction (in the radial direction of the rotation about the rotation axis line) is measured with respect to the rotation angle θi of the rotation base about the rotation axis line. Thus, change in distance from the geometric center of the lens shape to the feeler is measured as radii ρi.
In a measurement using such a conventional lens shape measuring apparatus, just before left and right spectacle lens frames are held by a frame holding section and the shape thereof is measured, the feeler mounted on the slider is arranged at a position corresponding to a geometric center of a left or right lens frame of spectacles having average-sized lens frames and having a distance between geometric centers of the left and right lens frames (frame pupil distance: FPD) in an average range. Then, this feeler is brought into contact with a measurement starting position of a lower rim part of the lens frame. Note that the maximum moving amount of this feeler in the horizontal direction (in the radial direction of the rotation about the rotation axis line) from the position immediately before the start of a measurement is predetermined.
While the rotation base is rotated horizontally about a vertical axis, amounts of horizontal movement of the feeler from the contact position of the feeler with the lower rim part with respect to rotation angles θi about the vertical axis of the rotation base are measured as radii ρi, so that lens shape data (θi, ρi) for the lens frame is obtained.
The larger the sizes of lens frame shapes (lens shapes) of left and right lens frames, the longer the distance FPD between the geometric centers of the left and right spectacle lens frames. For this reason, there has been a problem that, the larger the lens frames relative to those of average-sized spectacles, the larger the discrepancy between the setting position of the feeler immediately before the start of the measurement and the position of the geometric center of one of the lens frames.
Further, the conventional lens shape measuring apparatus as described above has the following problem because the maximum moving amount of the feeler in the horizontal direction (in the radial direction of the rotation about the rotation axis line) is predetermined. Specifically, in a lens frame shape measurement on a lens frame of large spectacles whose distance between the geometric centers of the left and right lens frames, i.e., FPD, is long, if the measurement is started at a measurement start position which is set for measurement on spectacles having average-sized lens frames, the feeler may get out of contact with the lens fitting groove in some cases. Likewise, in a measurement on a template for lens frames of large spectacles whose distance between the geometric centers of the left and right lens frames, i.e., FPD, is long, if the measurement is started at the measurement start position, the feeler stops and no further measurement on the template is possible because of the predetermined maximum moving amount of the feeler in the horizontal direction.
A larger maximum moving amount of the feeler in the horizontal direction (in the radial direction of the rotation about the rotation axis line) can prevent such problems. In such a case, however, a measurement unit of the lens shape measuring apparatus is larger in size, and consequently the lens shape measuring apparatus as a whole is larger in size.